如何在公共函数中被覆盖的公共函数中访问私有变量

Question

For example

var MyClass = function(){

  var that = this;

  var my_var = "I want this";

  var another_var = "this one is easy";

  this.aPublicFunc = function(my_var){

    console.log(my_var);   // logs "I don't want this";
    console.log(another_var);  // logs "this one is easy";
    console.log(this.my_var);  // logs undefined which makes sense as the this context is the context of the calling function.
    console.log(that.my_var);  // logs undefined
  };
};

var an_object = new MyClass();
var an_object.aPublicFunc("I don't want this");

Answer 1

Don't override it. It makes the code less readable and more confusing.

Answer 2

Private variables like you have with my_var are only accessible from code in the constructor and from the functions defined inside their scope (like in aPublicFunc() ) when it is called. And, to access them, you have to use a normal javascript reference to them. When you define an argument to aPublicFunc() with the same name, you hide that outer scope variable and there is NO way to reach it as defined. Those private variables are not members of the object, they are variables captured in a closure. In javascript, the only way to reach variables in a closure is from code in the scope of that closure and you can only reach them if nothing has overridden their name.

Your simple solution is to change the name of the argument or the local variable to something slightly different. If you really want them to look similar, then put an underscore in front of one of them like this:

var MyClass = function(){

  var that = this;
  var _my_var = "I want this";
  var _another_var = "this one is easy";

  this.aPublicFunc = function(my_var){

    console.log(_my_var);   // logs "I want this";
    console.log(_another_var);  // logs "this one is easy";
    console.log(my_var);  // logs "I don't want this"
  };
};

var an_object = new MyClass();
var an_object.aPublicFunc("I don't want this");

or make the argument a bit more obvious like this:

var MyClass = function(){

  var that = this;
  var my_var = "I want this";
  var another_var = "this one is easy";

  this.aPublicFunc = function(new_my_var){

    console.log(my_var);   // logs "I want this";
    console.log(another_var);  // logs "this one is easy";
    console.log(new_my_var);  // logs "I don't want this"
  };
};

var an_object = new MyClass();
var an_object.aPublicFunc("I don't want this");

You can see this last one work here: http://jsfiddle.net/jfriend00/Jeaaz/